1. vulgar slang To exert oneself to the utmost degree; to put forth the maximum amount of effort or strain. "Balls" is slang for the testicles, so the phrase in every meaning is usually (but not solely) said of or by a man. I've been breaking my balls trying to get the new software ready by the release date. Don't break your balls getting over here, there's no rush.

2. vulgar slang To harass, harangue, or pressure one about something, especially for a lengthy period of time. The boss has been breaking our balls over the number of sales our department has made this quarter. I said I would get it done today. Quit breaking my balls!

3. vulgar slang To tease one; to give one a hard time. Aw, come on, dude, I was just breaking your balls. No need to get upset about it.